The term electrophilic addition refers to the addition of electrophiles to which substrates?

• A. Alkanes
• B. Amines
• C. Alkenes
• D. Alkynes

Answer: (C)

Electrophilic addition is all about adding an electrophile to an unsaturated bond, specifically the π bond of a carbon–carbon double bond. The π electrons are regions of high electron density that the electrophile can attack, forming a new bond to one carbon and generating a carbocation-like intermediate, which a nucleophile then completes. Alkanes don’t have a π bond, so they aren’t sites for electrophilic addition under normal conditions. Amines aren’t substrates for this type of addition either; they’re more often involved as bases or nucleophiles. Alkynes do have π bonds and can undergo electrophilic addition too, but the standard, most familiar context is addition to alkenes. So the substrate class described by electrophilic addition is alkenes.